1. Field of the Invention
The present invention relates to a hard disk drive, and more particularly, to a method and apparatus for controlling a write current in a hard disk drive in order to improve an adjacent track erasure (ATE) property of the hard disk drive.
2. Description of the Related Art
A hard disk drive is an auxiliary storage apparatus of a computer used to read or write data from or to a magnetic layer of a hard disk with a magnetic head.
A writing magnetic head of a conventional hard disk drive is made of a metallic material, typically, a permalloy of 80% Ni and 20% Fe. A head slider for supporting the writing magnetic head is made of a non-metallic material.
Accordingly, when a write current flows though a metallic recording coil of the head, heat is generated. Due to a difference in thermal expansion coefficients between metallic and non-metallic materials, a thermal pole-tip protrusion (TPTP) phenomenon occurs, where parts around poles of the head protrude.
As is well known, the amount of the TPTP is proportional to I2R. Here, I denotes a current in the recording coil, and R denotes a resistance of the recording coil. In order to reduce the TPTP, it is necessary to reduce the current and the resistance R of the recording coil. The resistance R of the recording coil is a factor usually fixed during the production of the head. On the other hand, the current I is based on a write current and an over shoot current. Since the amount of the TPTP is proportional to the square of the current I, the TPTP is more sensitive to the current I than the resistance R.
As hard disk drives have higher densities, a track per inch (TPI) in the hard disk drives also increases. As a result, interference between tracks has been an important factor intensively considered during the design of the hard disk drive.
In other words, it becomes more difficult to stay below an adjacent track erasure (ATE) property threshold, as well as to secure a track margin. The ATE property threshold refers to a maximum allowable amount of adjacent tracks that are erased when a recording operation is performed on a track. A hard disk drive head with at most less than the ATE property threshold can be considered to be in a normal state, i.e., a non-ATE head. Conversely, a hard disk drive head that has an ATE property greater than the ATE property threshold would be considered in an ATE state, i.e., an ATE head. A head in an ATE state can further be considered to be ATE saturated.